How do I apply a discount to the whole checkout screen?

This article describes how to apply a discount to all the products in the Shopping Cart, as opposed to applying a discount to each product individually.

To discount multiple items in the Shopping Cart, the products must first be added. Add the desired products then, toward the bottom and to the left of CHECKOUT, hit the DISCOUNT button.

This brings up the Cart Discount screen. To apply a percentage discount, add the percentage to the box at the left OR choose a Promotion from the Select Promotion drop-down.  After a percentage discount or a Promotion is entered, hit APPLY.

Note that the discount has now been applied to all products currently in the Cart. You can now select CHECKOUT to complete the transaction.